Balance Sheet Account Details

The following table summarizes the various investment categories at December 31, 2018 and 2017 (in thousands):

Cost

Gross unrealized

gains

Gross unrealized

losses

Estimated

fair value

December 31, 2018

Short-term investments

Bank deposits

$

311,066

$

26

$

(29)

$

311,063

Corporate bonds

53,223

1

(45)

53,179

Corporate equity securities

135

1,191

—

1,326

Commercial paper

225,731

8

(76)

225,663

U.S. Government bonds

7,982

—

(9)

7,973

Municipal bonds

2,017

—

(4)

2,013

$

600,154

$

1,226

$

(163)

$

601,217

December 31, 2017

Short-term investments

Bank deposits

$

80,095

$

6

$

(42)

$

80,059

Corporate bonds

55,335

—

(96)

55,239

Corporate equity securities

207

1689

—

1,896

Commercial paper

27,933

—

(20)

27,913

Agency bonds

4,991

—

(1)

4,990

U.S. Government bonds

8,939

—

(10)

8,929

Municipal bonds

2,028

—

(13)

2,015

$

179,528

$

1,695

$

(182)

$

181,041

Other current assets consist of the following (in thousands):

December 31,

2018

2017

Restricted cash

$

2,616

$

—

Investment in Viking warrants

9,257

—

Other

8,545

1,514

$

20,418

$

1,514

Property and equipment is stated at cost and consists of the following (in thousands):

December 31,

2018

2017

Lab and office equipment

$

4,183

$

3,460

Leasehold improvements

2,418

1,917

Computer equipment and software

936

697

7,537

6,074

Less accumulated depreciation and amortization

(2,165)

(1,862)

$

5,372

$

4,212

Depreciation of equipment is computed using the straight-line method over the estimated useful lives of the assets which range from three to ten years. Leasehold improvements are amortized using the straight-line method over their estimated useful lives or their related lease term, whichever is shorter. Depreciation expense of $0.9 million, $0.4 million, and $0.2 million was recognized for the years ended December 31, 2018, 2017, and 2016, respectively, and is included in operating expenses.

Goodwill and identifiable intangible assets consist of the following (in thousands):

December 31,

2018

2017

Indefinite lived intangible assets

IPR&D

$

—

$

7,923

Goodwill

86,646

85,959

Definite lived intangible assets

Complete technology

235,413

222,900

Less: Accumulated amortization

(35,070)

(23,301)

Trade name

2,642

2,642

Less: Accumulated amortization

(1,048)

(916)

Customer relationships

29,600

29,600

Less: Accumulated amortization

(11,744)

(10,264)

Total goodwill and other identifiable intangible assets, net

$

306,439

$

314,543

Amortization of finite lived intangible assets is computed using the straight-line method over the estimated useful life of the asset of 20 years. Amortization expense of $15.8 million, $11.3 million, and $10.6 million was recognized for the years ended December 31, 2018 and 2017, and 2016, respectively. Estimated amortization expense for the years ending December 31, 2018 through 2023 is $13.6 million per year. For each of the years ended December 31, 2018, 2017, and 2016, there was no impairment of intangible assets with finite lives.

Accrued liabilities consist of the following (in thousands):

December 31,

2018

2017

Compensation

$

4,045

$

4,085

Legal

942

430

Amounts owed to former licensees

428

396

Royalties owed to third parties

1,025

954

Payments due to broker for share repurchases

4,613

—

Return reserve

3,590

—

Restructuring

1,093

—

Other

3,464

1,512

$

19,200

$

7,377

Contingent liabilities:

In connection with the acquisition of CyDex in January 2011, we issued a series of CVRs and also assumed certain contingent liabilities. We may be required to make additional payments upon achievement of certain clinical and regulatory milestones to the CyDex shareholders and former license holders. We paid CyDex shareholders, through 2016, 20% of all CyDex-related revenue, but only to the extent that, and beginning only when, CyDex-related revenue for the year exceeds $15.0 million; plus an additional 10% of all CyDex-related revenue recognized during such year, but only to the extent, and beginning only when aggregate CyDex-related revenue for such year exceeds $35.0 million.

In connection with the acquisition of Metabasis in January 2010, we entered into four CVR agreements with Metabasis shareholders. The CVRs entitle the holders to cash payments as frequently as every six months as proceeds are received by us upon the sale or licensing of any of the Metabasis drug development programs and upon the achievement of specified milestones.

The following table summarizes contingent liabilities as of December 2018 and 2017 (in thousands):